He has the problem of yawning a great deal whilst praying – what should he do?

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Check below answers in case you are looking for other related questions:
Obligation of making the rows straight
Ruling on counting the number of rak‘ahs on the fingers whilst praying

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Related Answers:
One who joined the prayer late is praying alone and he should not let anyone pass in front of him
The hadeeth, “There is no prayer for the one who lets his garment hang below his ankles”, and the ruling on the prayer of one who lets his garment hang below his ankles
Ruling on taking a Mus-haf from the mosque, elongating the back excessively during prostration, and fidgeting during prayer
Obligation of making the rows straight
Ruling on counting the number of rak‘ahs on the fingers whilst praying

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